Process for dewaxing mineral oils



Patented Oct. 17, 1939 7 2,176,623 PROCESS FOR DEWAXING MINERAL OILS Merrell R. Fenske, State College, Pa., assignor to Pennsylvania Petroleum Research Corporation, a corporation of Pennsylvania No Drawing.

10 Claims.

This invention pertains to the removal of solids and/or semi-solids from solution in liquids, and pertains particularly to the removal of wax from petroleum oil and/or fractions thereof. The invention pertains more particularly to the dewaxing of paraffin base lubricating oils such as those of Pennsylvania grade.

There are many methods and apparatus for the dewaxing of paraffin-bearing mineral oils as is evidenced, for instance, by the large number of issued patents in this art.

A large number of these processes center around the step of chilling or refrigerating the wax-bearing oil to precipitate wax from solution.

Separation of the solid or semi-solid wax from the remaining liquid may be effected by any suitable means such as by filter presses, centrifugal machines, etc.

In order to produce an oil of fairly low pour point, considerable refrigeration is required and,

since the temperature must be carried far below the freezing point of water, such refrigeration is relatively costly.

The invention herein is of a character which adapts it to be used by itself or in combination with a large number of processes of the prior art, or with steps of such processes and particularly with those which include cooling of the oil. With this invention, to effect the same result, lesser quantities of heat need be removed per unit vol ume of oil, and the temperature at which heat units are removed may be considerably higher, thus making it unnecessary to use extremes in refrigeration. In fact, some wax may be sepa- ';.35 rated without any removal of heat, and with the removal of heat the pour point may be depressed considerably below the temperature at which heat is removed, if desired. I V

In accordance with this invention, the oil is 4 subjected to a relatively high pressure, for instance, a pressure between several atmospheres and as many atmospheres as it is possible to produce, and more particularly between severalhundred and a thousand or more atmospheres.

A characteristic of parafiin wax, either amorphous or crystalline, is that, when it is dissolved in a menstruum such as petroleum oil, its mass per unit volume is less than its mass per unit volume when it is in the solidified state. In other words, the wax occupies less volume per unit mass when not in solution. Perhaps a better way of stating this is to say that when the wax is in solution in the oil, the total volume occupied by the wax and oil is greater than thetotal volume occupied by the waxand oil when the wax Application December 15, 1934, Serial No. 757,733

and oil exist as two separate phases. Therefore, as a result of subjecting the wax-containing oil to high compressive forces, the state of stress becomes such'that wax will separate from solution. 5

Heat of fusion is liberated when the wax solidifies. This raises the solvent capacity of the menstruum thus reducing the amount of solidified wax.

If the system were adiabatic a return of the pressure to the starting point would cause the wax to go back into solution and reabsorb the heat of fusion released upon solidification thus bringing the temperature back to the starting point.

Wax might be mechanically separated from the oil after release of the pressure and before the wax has time to go backinto solution.

If, however, heat is removed from the above system, say for instance, to hold the system at its starting temperature, large quantities of wax may be thrown out of solution, the quantity in any case being a function of the pressure.

Separation of the wax from the oil may be effected while the system. is still under pressure; 5 or after such pressure has been wholly or partially released, since, although upon a partial or total release of the pressure, a part of the wax will tend to redissolve, the rate of solution will be greatly decreased due to the absorption 011.30 heat of fusion.

Some re-solution of wax might be desirable in some instances, particularly in cases where less soluble wax components have remained in solution and more soluble wax components have been 35 precipitated. The re-solution of more soluble Wax components will cause less soluble wax components to precipitate.

Since the time element is involved, if separation of the wax from the surrounding liquid immediately follows a partial or total release of pressure, it is quite obvious that lesser quantities of wax will go back into solution.

It is desirable to have a relatively large difference in density between the wax and the menstruum from which the wax is precipitated.

Any suitable diluent known in the art may be added to the oil for the purpose of decreasing the density of the menstruum.

Such diluents might be, for instance, the low' boiling saturated paraflinic hydrocarbons and mixtures of these with or without their corresponding unsaturated derivatives. Because of the high pressures employed, normally gaseous hydrocarbons, such as methane, ethane, propane,

butane, ethylene, propylene, butylene, etc. may be employed, as well as any other normally gaseous substance which is liquid at the pressures employed and is capable of producing the desired results. If desired, additional refrigeration. may be obtained upon a partial or total release of the pressure when normally gaseous substances are employed.

Tertiary amyl alcohol is an excellent diluent particularly with heavy lubricating oil fractions of Pennsylvania grade.

It will be appreciated that in the process for dewaxing lubricating oils, I may add a diluent to the oil to reduce the density thereof and then subject the oil to a pressure suflici'ently high to cause wax to precipitate and remove the liberated heat of fusion from the :oil.

Any means known in the art may be employed in conjunction with the application of pressure to the oil to facilitate the precipitation and separation of wax such as seeding agents, filter aids, etc. This process may be used in combination with any other dewaxing process or in combination with any number of steps thereof, provided such combination is not wholly inconsistent with the fundamental features hereof.

By the use of this process, the pour point of an oil may be very materially reduced. For instance, a lowering in pour point of up to 15F. or more may be obtained per 500 atmospheres applied pressure, depending upon (1) the diluent used with the oil (2) the type of wax to be precipitated, whether amorphous or crystalline (3) the temperature level maintained (4) the type of oil (paraffin or mixed base) and (5) the viscosity of the oil (wax distillate or cylinder stock, neutral or bright stock).

With mixed base or asphalt base oils, substances other than wax may be separated by the same process.

Any means known in the art may be employed for applying pressure to the wax-bearing oil. For instance, this pressure might be established pneumatically. However, due to the fact that oil and wax are relatively incompressible as compared to gases, for economy in work units, the pressure would be applied directly to the oil, for instance, by mechanical means.

One way of mechanically applying high pressure to liquids is to fill a closed container of sufficient strength to withstand the pressure and to apply thepressure to the oil through the medium of a screw which enters the container. By careful machining of the screw, losses due to leakage may be maintained at a minimum.

Any other means may be employed for subjecting the oil to the desired pressure.

From the foregoing, it will be seen that by the application of pressure to the oil wax may be removed with or without cooling the oil; that through the application of cooling means the temperature level may be maintained at any desired point above, at, or below the starting temperature; and that by a combination of pressure and cooling the pour point of the oil may be adjusted as desired.

It is to be understood that the particular description herein is by Way of illustration and that changes, omissions, additions, substitutions and/or modifications may be made within the .scope of the claims without departing from the spirit of the invention which is intended to be limited only as required by the prior art.

I claim:

1. In a process for the removal of normally solid Wax components from liquid solution in a mineral oil, said normally solid wax components being of a character such that the total volume occupied by wax and oil when said wax is in solution in said oil is greater than when said wax and oil exist as separate phases, the steps of subjecting said solution of wax and oil to a sufficiently high pressure to cause said normally solid wax components to separate as a separate solid phase from solution in said oil due to the high compressive stresses set up throughout said wax and oil by said applied pressure, removing at least a part of the latent heat of fusion which is liberated as the result of the solidification under these conditions of said normally solid wax components, and removing said separated solid wax components from said oil.

2. In a process for the removal of wax in the solid phase from liquid solution in a lubricating oil, the steps of subjecting said oil to a sufficiently high pressure to cause said wax components to separate in the solid state from liquid solution in said oil by virtue of the high compressive stresses set up by said applied pressure, removing at least a part of the heat of fusion liberated during and due to change in said wax from the liquid to the solid phase, and removing said separated wax from said oil.

3. In a process for the removal of wax in the solid phase from liquid solution in a lubricating r oil of Pennsylvania grade, the steps of subjecting said oil to a sufficiently high pressure to cause said wax components to separate in the solid state from liquid solution in said oil by virtue of the high compressive stresses set up by .said applied pressure, removing at least a part of the heat of fusion liberated during and due to change in said wax from the liquid to the solid .phase, and removing said separated wax from said oil.

4. In a process for separating wax components from a solution thereof in lubricating oil, the steps of applying pressure to said solution sufficiently high to cause said wax components to separate from said solution by virtue of the high, compressive stresses set up by said applied pres sure, and simultaneously removing from said oil heat of fusion liberated during said separation.

5. In a process for dewaxing a lubricating oil,

the steps of adding a diluent to said oil to reduce;

the density thereof, then applying to said oil with diluent in solution a pressure sufficiently high to cause the wax to change by virtue of said applied pressure from the liquid to the solid phase with liberation of heat-of fusion, and removing heat of fusion from said oil to increase the quantity of wax separated at the applied pressure.

6. In a process for dewaxing a lubricating oil of Pennsylvania grade, the steps of adding a diluent to said oilto reduce the density thereof, then applying a pressure to said oil with diluent in solution sufficiently high to cause wax to separate from said oil in the solid phase with liberation of heat of fusion, increasing the quantity of.

wax thus separated by reducing the temperature of said oil, and removing said separated wax from said oil.

7. In aprocess for the removal 'of wax components in the solid phase from liquid solution in a:

lubricating oil, such wax components being of 'a character such that the 'total volume of wax and oil is greater when said wax is in said solution than when said wax is 'in a separated solidified state, "the steps of adding a diluent to said oil to reduce the viscosity and density thereof, applying a pressure to said mixture of the order of at least a hundred atmospheres and sufiiciently high to cause wax components to separate in the solid phase from liquid solution in said mixture by virtue of the high compressive stresses set up by said applied pressure, said separation being accompanied by the liberation of heat of fusion, removing heat from said mixture until at least a part of said liberated heat of fusion has been removed, and separating the solidified wax from said mixture.

8. In a process for the removal of wax components in the solid phase from liquid solution in a lubricating oil, such wax components being of a character such that the total volume of wax and oil is greater when said wax is in said solution than when said wax is in a separated solidified state, the steps of adding a diluent to said oil to reduce the viscosity and density thereof, applying a pressure to said mixture of the order of at least several hundred atmospheres and sufiiciently high to cause wax components to separate in the solid phase from liquid solution in said mixture by virtue of the high compressive stresses set up by said applied pressure, said separation being accompanied by the liberation of heat of fusion, removing heat from said mixture until at least a part of said liberated heat of fusion has been removed, and separating the solidified wax from said mixture.

9. In a process for the removal of wax components in the solid phase from liquid solution in a lubricating oil, such wax components being of a character such that the total volume of wax and oil is greater when said wax is in said solution than when said wax is in a separated solidified state, the steps of adding a diluent to said oil to reduce the viscosity and density thereof, adding a seeding agent to facilitate separation of said wax, applying a pressure to said mixture of the order'of at least a hundred atmospheres and sufficiently high to cause wax components to separate in the solid phase from liquid solution in said mixture by virtue of the high compressive stresses set up by said applied pressure, said separation being accompanied by the liberation of heat of fusion, removing heat from said mixture until at least a part of said liberated heat of fusion has been removed, and separating the solidified wax from said mixture.

10. In a process for the removal of normally solid wax components from liquid solution in a menstruum such as mineral oil, said normally solid wax components being of a character such that the total volume of wax and menstruum is greater when said wax is dissolved in said menstruum than when said wax is in a separated solidified state, the steps of subjecting said solution to a sufiiciently high pressure to cause said normally solid wax components to separate in a solid state from solution in said menstruum by virtue of the high compressivestresses set up by said applied pressure, and removing said separated solid wax components from said menstruum.

' MERRELL R. FENSKE. 

